On spindle picking cotton harvesters, the synchronization between the ground speed and the picking unit drum speed is critical to achieve optimal picking efficiency and cotton quality. Current harvesters synchronize the ground speed to unit speed using mechanical methods such as gear drives through the ground drive transmission and mechanical linkages between hydro pumps. Mechanical systems typically provide a linear relationship between ground speed and unit speed, and synchronization can only occur in one gear range. Synchronization is lost when the transmission shifts gear or the harvester is turned from the forward direction. In addition, ground speed and unit speed synchronization is lost over time because of efficiency changes; tolerance stack-up, and part wear including tire tread wear. Improper synchronization adversely affects field efficiency and harvested cotton quality.
The mechanical drive systems do not allow easy adjustment of speed ratios to accommodate for variable field and plant conditions. For example, in heavy cotton conditions, the operator may wish to increase picker drum speed relative to row unit ground speed to increase the picker spindle density in the crop. In low yield cotton, the operator often increases harvester speed, but a proportional increase in drum speed may not be warranted since there is less cotton to engage in the row. Over-speed of the picking units increases component wear.
Current mechanical drive based systems allow the units to rotate in reverse when the machine is moved in reverse. Such operation in reverse can cause the slip clutch to activate and can drag cotton backwards against the moistener columns and doffers to adversely affect picking unit adjustment. To prevent this, the operator performs a complicated procedure which includes disengaging the units, backing up, stopping, engaging the units, and then proceeding in the forward direction.
Present mechanical drive systems require complex linkages and a relatively large number of moving parts. A direct linkage drive to the row units also allows the units to be driven when the hydro control handle is moved out of neutral position.